1. Field of the Invention
This invention relates to an apparatus for conveying a sheet such as an original and at the same time, reading images such as characters formed on the sheet. The apparatus of this type is often used, for example, in a facsimile apparatus or the like.
2. Related Background Art
An apparatus of this type has been disclosed, for example, in U.S. Pat. No. 4,438,918. In this apparatus, a sheet (an original) is conveyed along a predetermined conveyance path by conveying rollers. A slit is provided in the course of the conveyance path, and a light is applied to the original through the slit and the reflected light therefrom is imaged on an image sensor by a lens to thereby read the image of the original. The image sensor comprises a photoelectric conversion element disposed on a base plate widthwisely of the original, and the reflected light from the original is received and converted into an electrical signal by the photoelectric conversion element.
In such an apparatus, however, the image sensor can be disposed at a location within the apparatus into which it is difficult for the outside light to enter but a lens, a reflecting mirror, etc. are required, and this leads to bulkiness in the apparatus.
Therefore, the applicants have developed a reading apparatus for reading the image of an original directly by an image sensor without the use of a lens, a reflecting mirror, etc. In this reading apparatus, a photoelectric conversion element is provided on a transparent plate disposed on a base plate having a hole for passing therethrough the light beam from a light source, and the photoelectric conversion element is covered with a protective transparent sheet. When the original is to be read, the reflected light of said light beam applied to the original being conveyed while contacting said protective transparent sheet is received and converted into an electrical signal by the photoelectric conversion element.
However, where the original is directly read in this manner by the photoelectric conversion element without the intermediary of a lens, the resolving power drops and the image becomes blurred if the original floats from the protective transparent sheet. To keep a high resolving power, it is necessary to use a conveying roller for conveying the original while urging the original against the protective transparent sheet and moreover to, make an array of photoelectric conversion elements (a reading line) arranged so as to cross the conveyance path coincident with the base plate of the conveying roller with high accuracy.
However, with a construction in which an image sensor is held on a base plate pivotably supported on a shaft parallel to the shaft of the conveying roller and the base plate is urged against the conveying roller, it is difficult to obtain high accuracy. That is, both the shaft of the conveying roller and the shaft of the base plate support the opposite ends and it is difficult to form a supporting hole in a support member at an accurate location. It is also conceivable to support the shaft of the base plate in a slot in order that the protective transparent sheet may be uniformly urged against the conveying roller, but again in that case, it is difficult to make the base line of the conveying roller coincident with the reading line.